Make HTTPClient follow redirects by default.

Closes #3875

The autoupdator, which uses `qutebrowser.misc.httpclient` has been failing recently because the URL that it hits to check version information is now serving a 301 moved permanently. By default QNetworkRequest doesn't follow redirects so it was getting back a (non-json, despite the request) body pointing to the new location, instead or version information. This changes fixes that by changing HTTPClient to use a QNetworkRequest subclass which follows redirects by default.

It lookes like HTTPClient is currently only used in autoupdate.py, version.py, and crashdialog.py so I don't expect any breakage.

5.6-5.8 Only had a boolean setting available which allows redirects, but not from the https scheme to http, 5.9 introduces a more nuanced setting. I have tested locally on 5.7.1 and 5.10.

qutebrowser/misc/httpclient.py

@@ -28,6 +28,21 @@ from PyQt5.QtNetwork import (QNetworkAccessManager, QNetworkRequest,
                              QNetworkReply)
 
 
+class HTTPRequest(QNetworkRequest):
+    """A QNetworkRquest that follows (secure) redirects by default."""
+
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        try:
+            self.setAttribute(QNetworkRequest.RedirectPolicyAttribute,
+                              QNetworkRequest.NoLessSafeRedirectPolicy)
+        except AttributeError:
+            # RedirectPolicyAttribute was introduced in 5.9 to replace
+            # FollowRedirectsAttribute.
+            self.setAttribute(QNetworkRequest.FollowRedirectsAttribute,
+                              True)
+
+
 class HTTPClient(QObject):
 
     """An HTTP client based on QNetworkAccessManager.
@@ -63,7 +78,7 @@ class HTTPClient(QObject):
         if data is None:
             data = {}
         encoded_data = urllib.parse.urlencode(data).encode('utf-8')
-        request = QNetworkRequest(url)
+        request = HTTPRequest(url)
         request.setHeader(QNetworkRequest.ContentTypeHeader,
                           'application/x-www-form-urlencoded;charset=utf-8')
         reply = self._nam.post(request, encoded_data)
@@ -77,7 +92,7 @@ class HTTPClient(QObject):
         Args:
             url: The URL to access, as QUrl.
         """
-        request = QNetworkRequest(url)
+        request = HTTPRequest(url)
         reply = self._nam.get(request)
         self._handle_reply(reply)